The invention relates to a process and an apparatus to monitor a yarn piecing joint on a spinning machine with a plurality of spinning stations to which a piecing robot equipped with a yarn piecing apparatus with adjustable yarn piecing speed can be presented, with each spinning station or the piecing robot having a yarn monitoring apparatus to monitor yarn quality.
In a known yarn or thread cleaner for an open-end spinning machine (German patent 39 28 417 A1) respective thickness tolerance thresholds for different length ranges are entered to monitor the yarn quality of the spun yarn. When the yarn thickness tolerance is exceeded, the affected segment of the yarn is cut out and the yarn is pieced anew. The quality criteria essentially depend on the length and the diameter of the spun yarn, so that the length of the measured yarn must be known precisely to judge whether the quality criterion for the corresponding length class has been met or not. The length is here measured by entering the yarn production speed of the spinning machine which is constant once the nominal yarn production speed has been reached, and by measuring the time. The yarn length then results by multiplying the time with the yarn draw-off speed. During the piecing phase the yarn is however accelerated from the yarn draw-off speed to the nominal production speed, so that here no constant yarn draw-off speed is determined. It is therefore not possible to classify yarn defects during the piecing phase, since the yarn cleaner is lacking information concerning yarn length.
In a known apparatus of this type to monitor a yarn piecing joint on a spinning machine (German patent 40 30 100 A1), a yarn-monitoring device is installed at each spinning station to monitor yarn thickness during running production. During the piecing of the yarn by a piecing robot that can be presented to a spinning station, the yarn thickness is monitored by means of a second yarn-monitoring device that is built into the automatic spinning unit. On the one hand quality control with respect to yarn thickness is carried out using the results of the second yarn monitoring apparatus, and on the other hand statistical data is collected to optimize the piecing process of the piecing robot. In both instances, measuring data is used that is taken several centimeters upstream and downstream on the yarn from the yarn-piecing joint. The start and the end of measuring is determined by the start of the rotor run-up and the rotor acceleration. However, an additional measurement of the rotor speed is necessary for this. It is however not possible in that case to take into account the exact yarn position of the piecing joint of the current speed of the yarn to determine the yarn defect per length unit.
In a known method to monitor yarn quality of a yarn piecing joint (German patent 196 49 314 A1) the thickness profile of the yarn is also measured a few centimeters before and after a yarn piecing joint, and the measurement is then evaluated based and the precise position of the yarn piecing joint is determined on basis of that evaluation and the quality of the yarn piecing joint is judged by different criteria. In the evaluation it is assumed that the distance between two measuring points measured by the yarn monitoring device along the yarn can be associated with a predetermined measuring resolution without taking into account that the yarn length between two measuring points changes due to the acceleration in the acceleration phase during piecing. The subsequent finding of a yarn-piecing joint based on several measuring points is very time sensitive and therefore results in a delayed recognition of a defect on the yarn-piecing joint or in the adjoining yarn areas. Furthermore, because of the imprecise tarn length assignment to the measuring points, an exact determination of the yarn length defects is not possible.
It is therefore a principal object of the invention to provide a method and an apparatus to monitor a yarn piecing joint on a spinning machine by means of which simple and precise establishment of the relationship between tarn piecing joint and measuring time or measured value and a precise classification of length and thickness defects in the yarn are possible. Additional objects and advantages of the invention will be set forth in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In an embodiment of the apparatus to monitor a yarn-piecing joint according to the invention, a yarn monitoring apparatus to monitor the yarn quality is installed on a piecing robot or at every spinning station of the spinning machine. Following a yarn breakage or for a bobbin replacement at a spinning station, the piecing robot can be presented to the spinning station, this piecing unit carrying out piecing of the yarn at the piecing station in a known manner.
Based on the piecing values set and optimizable on the piecing robot, the evolution of speed, over time, of the yarn draw-off, i.e. the velocity profile, is calculated in advance from the machine parameters of the piecing robot. Thanks to the transmission of piecing parameters of the piecing robot via a communication system to the yarn monitoring apparatus, the latter receives information concerning the progression of the yarn draw-off during piecing. The piecing parameters can in that case be transmitted continuously in the piecing phase from the piecing robot to the yarn monitoring apparatus, either before the beginning of piecing or at the beginning of piecing.
The piecing parameters may comprise a complete time profile of velocity or only individual acceleration, speed and/or time data from which a velocity-time profile or a yarn position-time profile is calculated first in the yarn monitoring apparatus. Based on the distance from the yarn piecing point to the yarn monitoring apparatus and on the velocity profile, the time can be calculated when the yarn piecing joint runs through the yarn monitoring apparatus. Thereby the characteristic yarn data obtained by the yarn monitoring apparatus can be assigned to the yarn-piecing joint, to the upper yarn of the yarn used for piecing and to the yarn segment following the piecing joint. Derived magnitudes, such as a length-dependent yarn thickness defect, can therefore be calculated exactly.
Additional piecing parameters to be taken into account in the evaluation can be the length of the piecing joint that depends among other things on the drawing-off speed and the rotor diameter at the spinning station. From the starting point and/or the end point of the yarn piecing joint or some other reference value, the yarn monitoring apparatus can then assign the measured values to the yarn-piecing joint via the directly received yarn piecing length or from the calculated yarn piecing length.
The yarn monitoring apparatus to monitor the yarn quality during piecing can in this case be provided at the piecing robot, at the spinning station, or at both. In the latter case, quality monitoring can be carried out at will with either of the two yarn-monitoring apparatuses.
If a yarn monitoring apparatus is provided only at the spinning station, it is used to measure the yarn piecing joint as well as the running yarn. Therefore the manufacturing costs of the spinning machine are reduced and the control expenditure for the spinning machine is simplified considerably since no control device or communication line is necessary for a yarn monitoring apparatus at the automatic spinning unit.
The yarn quality monitored by the yarn monitoring apparatus is in this case preferably the yarn thickness which can be determined e.g. optically. Additional quality parameters that can be monitored alternatively or in addition by the yarn monitoring apparatus are the yarn mass per yarn length that can be determined capacitively for example, spectral properties in order to detect e.g. foreign matters in the yarn, the surface aspect, e.g. as a measure of the emergence of fiber ends from the yarn, which is measured via reflection or distribution, or other physical characteristics.
At the spinning station and/or at the piecing robot it is also possible to provide several yarn monitoring apparatuses, each to monitor different quality parameters of the yarn. The yarn monitoring apparatuses for the different parameters may have common or separate measuring heads and common or separate controls, whereby the latter then receive the piecing parameters of the piecing robot separately, or exchange the calculated velocity profiles.
The yarn monitoring apparatus can in this case be integrated into a modular assembly in which the acquisition of physical measured values of the yarn as well as the evaluation of the measured values, the evaluation of the transmitted piecing parameters and, if applicable, the triggering of a yarn cleaning signal take place. Alternatively, e.g. the acquisition of measured values and their evaluation can take place in separate modular groups or be transferred to other components such as the central controls of the spinning station or spinning machine.
Due to the precise monitoring of yarn quality the optimizing of the piecing process is improved by using the statistical material of the monitoring of the yarn piecing joint so that optimizing is already possible with few measured data and finally the yarn quality can be improved by the greater precision of the optimizing process.
The communication system is in this case ordinarily a communication bus system of the spinning machine through which the controls of the piecing robot transmits piecing parameters to the controls of the monitoring apparatus. Alternatively a direct communication connection between the piecing robot and the yarn monitoring apparatus can be provided. In addition, further parameters such as e.g. the rotor diameter or the nominal yarn production speed can be made available by the central controls of the spinning machine or the spinning station.
A time-dependent piecing speed profile is obtained from the piecing parameters by means of an evaluation unit of the yarn monitoring apparatus, so that the drawing-off speed is known at any point in time and, derived from it, the position of the yarn at any point in time. Thereby a classification of a characteristic yarn value as a function of length can be made, i.e. the cutting out of a defective yarn segment can be initiated.
Upon linking the values calculated from the piecing parameters to the measured characteristic yarn values of the yarn monitoring apparatus, these are stored in a memory so that a statistic on the characteristic yarn values and their distribution can be obtained and used for the classification of the spun yarn and for quality monitoring of the individual spinning station.
If the result of the linkage between the values derived from the piecing parameters and the measured characteristic yarn values is compared to one or more limit values, a cleaning signal is obtained if the limit value is exceeded, causing the corresponding defective location on the yarn to be separated out of the running yarn material. This may be e.g. a defective yarn piecing joint or a thickness deviation in the spun yarn following the yarn-piecing joint.
The calculation of the position of the yarn piecing joint from the piecing parameters is especially improved, so that a differentiation is made between the yarn material near the piecing joint and the yarn material before and/or after the piecing joint. This differentiation can then be used to advantage in establishing separate statistics for the quality of the piecing joint by storing the data relating to it. This also makes it possible, when comparing limit values, to differentiate between the measured characteristic values pertaining to the yarn segment containing the yarn piecing joint and the yarn segment outside the piecing joint, so that different limit values are applied to the yarn piecing joint for quality adjustment. The defect tolerance for the piecing joint can therefore be raised so that, based on the small number of piecing joints over the entire yarn length, exceeding higher limit values is accepted while the limits of defect tolerance for the running yarn are narrowed.
In another embodiment, a running time delay of the communication transmission of the piecing parameters to the yarn monitoring apparatus is compensated for by means of a running time compensation parameter. Thereby synchronization between the piecing event and the assignment of the measured values of the actual yarn position is achieved, independently from the used communication system and its signal durations.
The running time compensation can take place e.g. in such manner that when the piecing parameters have been transmitted to the yarn monitoring apparatus, the beginning of piecing is delayed by a predetermined time span (compensation parameter) equal to the running time of the communication. In this case the compensation for synchronization is effected at the transmitter of the piecing parameters. Otherwise, the piecing start and the start of measuring at the yarn-monitoring apparatus are related to an absolute, common system time (compensation parameter). Furthermore, synchronization can be achieved in that a starting signal is transmitted to the yarn monitoring apparatus or from the yarn monitoring apparatus via a rapid direct communications connection at a reference point in time. A compensation for the running time can also take place at the recipient of the piecing parameters, whereby the yarn monitoring apparatus and possibly yarn cleaning system are activated only after the piecing start.
According to an embodiment of the method to monitor a yarn piecing joint during piecing on a spinning machine, piecing parameters of the piecing robot are also transmitted to a yarn monitoring apparatus so that the advantages described above can be achieved through the method.
In an advantageous embodiment of the method either the yarn quality of the upper yarn, i.e. of the yarn used for piecing, is not measured or the corresponding measured values are not stored. This reduces the quantity of data to be stored. Also, counting double possible defective spots of the upper yarn that should be acquired statistically is thus avoided, since the segment of the upper yarn has already gone through the yarn monitoring apparatus before a yarn breakage and runs again through the yarn monitoring apparatus after piecing.
If, according to an advantageous embodiment of the method, a starting signal is transmitted by the automatic spinning unit to the yarn monitoring apparatus at the moment of starting yarn draw-off, and if at the same time the piecing parameters of the piecing robot are transmitted, a precise synchronization between yarn draw-off and yarn quality measurement is achieved.
If a first point in time when the yarn piecing joint runs through the yarn monitoring apparatus, and a second point in time when the actual yarn draw-off speed reaches the nominal yarn draw-off speed are transmitted as piecing parameters to the yarn monitoring apparatus, the yarn draw-off speed or yarn position can be calculated at any point in time by using the data and an already stored, known yarn draw-off speed characteristic of the automatic yarn piecing unit.
With an alternate embodiment of the method the yarn draw-off speed of the piecing robot is calculated or measured and is continuously transmitted to the yarn monitoring apparatus. Thereby the calculation effort of the yarn monitoring apparatus is reduced and its evaluation electronics can be simplified. In order to determine the point of time when the yarn piecing joint runs through the yarn monitoring apparatus, a signal is transmitted in addition to the yarn draw-off speed data by the piecing robot to indicate the yarn piecing joint to the yarn monitoring apparatus. Thereby a differentiation of the characteristic yarn values from a segment of the yarn piecing joint and also of adjoining yarn segments can be made at the yarn monitoring apparatus.